Network communication systems are used for a wide variety of applications including voice and data services. For example, mobile communication systems utilize a variety of wired and wireless networked systems to provide communications between mobile handsets, landline telephones, IP (Internet Protocol) connected devices, and/or other communication devices. It is often desirable to monitor frequency and phase of signals being transmitted within network communication systems to determine if the communications are within accepted tolerances. For example, specifications for many mobile communication system standards require communications to have frequency deviations and/or phase deviations that are within predetermined limits.
Frequency synchronization for some mobile communication systems has previously been provided through the physical layer frequency of high-speed Time Division Multiplexed (TDM) communication links (e.g., E1 or T1 lines). Phase and frequency synchronization for some other mobile communication systems has previously been provided through the use of GPS (Global Positioning System) or other GNSS (Global Navigation Satellite System) timing signals. High-speed TDM communication links and/or satellite systems both provide physical layer timing signals for synchronizing mobile communication systems. However, in newer mobile communication systems, which make use of smaller, denser and lower cost base stations, such synchronization signals may not be available, reliable, cost-effective or practical (e.g., where T1 links are replaced with lower cost packet-based links; where satellite signals are deemed unreliable because they are vulnerable to jamming; or where satellite antennas are not possible or are cost prohibitive). Accordingly, some newer communication systems rely either wholly or partially upon packet-based time synchronization techniques, such as for example, PTP (Precision Time Protocol), CES (Circuit Emulation Service), SAToP (Structure-agnostic Time-Division-Multiplexing over Packet), or another packet-based timing protocol.
Frequency synchronization that is derived from the aforementioned physical layer signals is inherent in the level transitions of the signal itself (e.g., voltage transitions from logic “0” to logic “1”). By contrast, frequency and phase synchronization information that is to be derived from packet-timing-protocol based techniques is not inherent in the physical layer signal. Rather, such packet-timing-protocol based systems rely upon receiving packets, time-stamping them, and analyzing all packets being communicated within a packet flow, which can increase the processing requirements and cause delays. Further, packet layer impairments (e.g., packet loss and delay variation) adversely affect synchronization performance where packet-based timing protocols are utilized.
Phase synchronization is also used for some mobile communication systems, particularly newer systems. Timing for phase synchronization has traditionally been provided using GNSS timing signals. However, as indicated above, satellite systems are often not available or not practical (e.g., satellite antenna not possible or cost prohibitive). Newer systems have increasingly relied upon packet-based techniques such as PTP or NTP (Network Time Protocol) for phase synchronization. As indicated above, these timing-protocol based techniques rely upon receiving, time-stamping and analyzing all packets being communicated within a packet flow, which can lead to delays and significant processing requirements. Further, as above, packet layer impairments (e.g., packet loss and delay variation) adversely affect phase synchronization performance where packet-based timing protocols are utilized.
It is noted that in some circumstances wireless operators may rely on third party network operators to provide “backhaul” communications between a mobile site and a wireless packet core network. This use of third-party backhaul providers is more common in countries like the United States and less common in countries where the telecommunications networks are now or once were operated by an agency of the national government (sometimes known as the Postal, Telephone and Telegraph service, or PTT). Timing performance requirements for wireless backhaul systems are still being developed, and techniques for providing adequate measurements of backhaul performance are also yet to be fully developed.
With respect to the use of GNSS for timing synchronization, it is noted that certain characteristics of GNSS are problematic for some solutions. GNSS antennas/receivers, for example, may be impractical to physically implement and/or may be too costly. For example, from a cost perspective, GNSS receivers may be prohibitively expensive for small cells or applications. From a physical implementation perspective, antenna cabling may be difficult to install or may need to extend over long distances (e.g., cabling for a tall sky scraper). Antenna sites may also be costly or unavailable. Further, GNSS receivers can be vulnerable to jamming, and GNSS jammers are widely available. Other emerging threats to GNSS reliability include spoofing and meaconing. Accordingly, operators may not want to depend wholly or partly on GNSS for timing synchronization.
In addition, with respect to the use of GPS, which is a specific type of GNSS, it is noted that GPS is a system run by the United States Navy. Wireless network operators, and particularly those operators located in other countries, may be uncomfortable relying, in whole or in part, upon a United States military system to synchronize their civilian wireless networks. Accordingly, some operators may not want to depend on GPS for timing synchronization.
It is further noted that packet-based techniques for frequency and phase synchronization rely upon the ability of the communication equipment to transmit packets at precise instants in time, and upon the ability of the communication equipment to precisely record the instant in time when a packet arrives. The times of transmission and reception are referred to as time stamps. Packet-timing systems (e.g., NTP or PTP) follow defined protocols for transferring the necessary time information from a source network device to a destination network device. The destination network device then analyzes the packets and their time stamps so that the frequency or phase of the sink matches that of the source.
Because the performance of packet-based timing protocol techniques is not inherent in the physical layer signal, it can be more difficult to monitor its performance. And because the performance of packet-based timing protocol techniques can be impaired by packet loss and delay variation, it can be increasingly important to monitor their performance. Further, packet-layer impairments introduced by third-party backhaul operators may need to be measured at the point of demarcation for service assurance and fault localization. Accordingly, monitoring the performance of packet-timing-protocol based synchronization is both more important and more difficult than it has been in previous systems that relied upon physical-layer synchronization signals.
In short, frequency and/or phase synchronization is needed for a variety of network systems, including network voice and data communication systems. However, current solutions have undesirable reliability, cost, and delay disadvantages.